This invention relates to an indicator device for a vehicle in which characters, a scale, a pointer etc., are brightened by back light, and more particularly to a vehicle indicator device of the analog meter-type in which only characters, a scale etc., of a dial plate, as well as a pointer, are brightened utilizing critical angles of prisms.
Usually, in the daytime, a speedometer or the like of the analog meter-type used as a vehicle indicator device does not especially need illumination since it can be visually recognized thanks to the external light; however, in the night or in a tunnel, the device requires illumination since the outside is dark. Therefore, there is a conventional device as shown in FIG. 12 in which characters, a scale, a pointer and etc., are brightened by back light, also there is a conventional device of the reflection type as shown in FIG. 13.
In the device shown in FIG. 12, a light guide plate 43 is provided between an interior device 41 for driving a pointer 45 and a dial plate 42, and light from light source bulbs 44 is introduced into the light guide plate 43 from its ends 43a as indicated by arrows in the drawings, so that the light guide plate 43 is brightened at the back side of the dial plate 42, thereby brightening a light-transmitting scale etc., formed on the dial plate 42. With respect to the pointer 45, the light is applied from the light guide plate 43 to a boss 45a of the pointer 45 along the outer periphery of a pointer shaft 41a, so that the pointer 45 is brightened by the guidance and diffusion of the light within the pointer 45.
In the vehicle indicator device shown in FIG. 13, a light source bulb 54 is provided at the front upper side of a dial plate 52 and a pointer 55, and light is applied to the dial plate 52 and the pointer 55, and is reflected. Reference numeral 51 denotes a drive portion for the pointer 55.
However, when a vehicle, using the vehicle indicator device of the above illumination type, suddenly enters the dark, such as a tunnel, during the travel in the daytime, the degree of expansion of the irises of the eyes of the driver can not follow this change, and therefore before the eyes become adapted to it, the indication of the meter appears dark, and lacks in visibility. Further, when light, for example, of a headlamp is applied from a position in front of the vehicle, the irises of the driver's eyes become narrow, so that the meter appears dark, thus adversely affecting the visibility.
In such a case, the visibility can be enhanced by increasing the contrast and brightness of the meter; however, in the above conventional vehicle indicator devices, it is difficult to increase the brightness of the bulb to a level higher than the present level because of heat radiation and so on.